Electrostatic reproduction techniques



Oct. 4, 1966 FYLER 3,277,493

ELECTROSTATIC REPRODUCTION TECHNIQUES Filed Feb. 15, 1962 2 Sheets-Sheet l Oct. 4, 1966 N, FYLER 3,277,493

ELECTROSTATIC REPRODUCTION TECHNIQUES Filed Feb. 15, 1962 2 sheets'sheet 2 United States Patent 3,277,493 ELECTROSTATIC REPRODUCTION TECHNIQUES Norman F. Fyler, 1911 Oakdell Drive, Menlo Park, Calif. Filed Feb. 13, 1962, Ser. No. 172,945 9 Claims. (Cl. 346-74) This invention relates to electrostatic reproduction apparatus and methods, and deals with techniques using devices for applying electrostatic charge patterns to sheets, for example by means of a specific type of cathode ray tube, followed by developing the charge pattern to form a visible image in accordance with signals applied to the cathode ray tube. More particularly, the invention is concerned with improvements relating to techniques in sheets.

Reproduction apparatus of the type mentioned in the foregoing paragraph are well known in the art. Although different techniques for depositing charge patterns have been suggested, good results are generally obtained when using a specific type of cathode ray tube. Accordingly, the present invention may advantageously use a recently developed cathode ray tube, originally designed for the purpose of facsimile reproduction systems or the like. An improved cathode ray tube and reproduction techniques using it are described in copending United States patent application Ser. No. 16,734, filed March 22, 1960, Norman P. Fyler, now Pat. No. 2,193,907, and the essential structure of such tube is described in the following paragraph.

Conventional cathode ray tubes generally include a phosphor screen on which the electron beam impinges. The scanning motion of the electron beam is produced by changing electrostatic or magnetic fields, as is well known in the art. The specific tube used in accordance with certain embodiments of the present invention has no phosphor screen but is provided with a faceplate which transmits electrical charges to discrete zones or elemental areas. For this purpose, the faceplate of the cathode ray tube is provided with a plurality of individual conductors, generally a great number of wire sections, which traverse the faceplate. The faceplate itself is made of highly insulating material and the individual wire conductors extending through it are physically separated and also electrically insulated from each other.

In accordance with the specific use in facsimile apparatus or the like, the individual wires imbedded in insulating material to form the faceplate of this type of cathode ray tube are placed in a linear arrangement, generally a small number of rows of very closely spaced wire conductors, to form a narrow elongated strip-shaped faceplate, as described in the above mentioned copending application. The electron beam performs a sweeping motion along the internal surface of the faceplate to impinge on the internal wire ends, applying to them negative charges which change in accordance with modulation of the electron beam. These charges are transferred through the faceplate by the array of individual wires and deposited on a recording medium such as a dielectric film passed along the external surface of the faceplate. The charge pattern appearing on the recording medium is then rendered visible by any suitable known developing process.

According to the above mentioned copending United States patent application and a number of other techniques previously suggested, charge patterns are deposited on webs of recording medium supplied from rolls in a continuous manner. As is readily understood, the recording medium such as especially treated paper, for example, is initially threaded into the reproduction device and the step of threading need not be repeated until the supply from the roll is exhausted. Accordingly, the comparatively complicated manipulations associated with threading the starting end of the web into the device does not constitute a significant shortcoming. Furthermore, provided that the web is moved across the faceplate at constant speed, there is no need for otherwise synchronizing the tube operating circuitry, including the signal source, with the motion of the web.

However, considerable difficulties are encountered when individual sheets are used instead of a continuous web of recording medium. It will be apparent that for the purpose of continuous operation, when reproducing images on individual sheets, each of the sheets must be fed through the device, with the leading edge of each sheet being properly guided into the device. Care must be taken that the sheet is transported through the device at a constant speed, in a proper spartial relationship with respect to the faceplate of the cathode ray tube, and without buckling or other disturbances of motion which would result in a distortion of the image reproduced on the recording medium. A further important point is that synchronization between the tube operation and motion of the sheet passed across the faceplace of the tube is a necessary requirement for properly placing the image at the location of the sheet where it is intended to appear. In other words, the tube must start operating when the sheet is advanced into a predetermined position, generally at the beginning of the period of time in which the best is passed across the faceplate of the tube. In this regard, it should be noted that prior art devices of the type under consideration either do not provide for any possibility of automatically and continuously feeding individual sheets into the machine or, wherever reproduction on individual sheets is considered, the operator must carefully control the proper functioning of the machine. Accordingly, the need for an automatically synchronized reproduction machine which operates continuously and with a commercially acceptable speed remained unfilled up to the present time.

The foregoing paragraphs deal with the section of a reproduction machine in which a charge pattern is ap plied to a recording medium, such as a sheet of paper, and the following now refers to another section of the device in which the applied charge pattern is developed to render it visible, subsequently fixed.

It is well known in the art that charge patterns applied to recording mediums can be rendered visible by applying particulate material, which is preferably pre-charged, to the surface on which the charge pattern has been applied. Numerous types of reproduction machines, some of them designed for oflice use, are based on this principle, and the technique is frequently referred to as xerography. Considering that a complete reproduction machine of the type under consideration must include a developing section in which the latent charge pattern is rendered visible and suitably immediately fixed, the present invention includes improved techniques for applyin'g particulate material or powder to the individual-sheets. Such improvements include features described in more detail below which are essentially linked to the purpose of recording on individual sheets. It will be apparent that an otherwise efiicient powder applicator of the prior art, when used for the purpose contemplated herein, would have a tendency to continue blowing powder during the interval between sheets and, therefore, into the open air. More specifically, and referring now to one of the more important problems encountered when using individual sheets, it was found necessary to prevent spilling of particulate material during the intervals between the passage of consecutive sheets.

Accordingly, a general important object of the present invention is to provide an improved reproduction apparatus using individual sheets as the recording medium.

It is a further object of the present invention to fulfill the needs for synchronization in this type of reproduction machines when recording on individual sheets.

A still further object of the invention is the automation of the different steps involved in feeding individual sheets through a reproduction apparatus, as discussed in more detail below, and also of the operation of the cathode ray tube used for applying charge patterns on the individual sheets.

It is another object of the invention to smoothly and flawlessly feed the individual sheets across the faceplate to avoid buckling or any other disturbance in the motion of the sheet which would result in distortions of the charge pattern and consequently of the finished image.

A still further object of this invention is the improvement of powder applicators especially useful in reproduction machines using the xeorographic method and resulting in more contrasting images of the finished copies.

Another object of the invention is the adaptation of powder applicators for the specific purpose of developing images applied to individual sheets without sacrificing the improved contrast features resulting from a specific design described below.

In accordance with one illustrative embodiment of this invention, the section of a reproduction apparatus in which the charge pattern is applied includes a cathode ray tube having a charge-transmissive faceplate, as described above, power circuitry for operating the tube, and a signal source for modulating the beam intensity in accordance with signals received for applying a charge pattern to a recording medium. This section of the reproduction machine further includes an outer electrode facing the faceplate which assists in accelerating the charges to the recording medium and at the same time serves as a guide for the individual sheets consistituting the recording medium, in accordance with the purpose of the present invention. The outer electrode is mounted to pivot so that it may assume either of two positions; in one of the positions a gap is formed between the electrode and the tube, and in the second position the electrode is pivoted and biased toward the faceplate. The sheet-feeding mechanism of this embodiment may include at least three pairs of cooperating rollers, two of which are employed on opposite sides of the cathode ray tube, and the third being associated with one developing position of the apparatus. The first pair of rollers performs a pushing action on the sheet to forward it into the gap between the outer electrode and the faceplate of the tube. When the leading edge of the sheet has passed the faceplate, it is pushed between the rollers of the second pair, which now start exerting a pulling action on the sheet. At this moment, the pushing action of the first roller pair is stopped by means of a pair of contact elements associated with this second pair of rollers. This is preferably achieved by removing one of the pushing rollers from contact with the sheet. Simultaneously, the outer electrode is shifted into its second position in which the gap between it and the faceplate of the tube is substantially closed. As a result, the sheet is fed in a predetermined position with respect to the faceplate and practically in contact with it, the motion of the sheet being produced exclusively by the pulling action of the second pair of rollers. By virtue of this arrangement, smooth and undisturbed flawless motion of the sheet is assured. No buckling of the sheet can possibly occur as a result of the fact that only one pair of rollers contributes to the transportation of the sheet. At this point it should be mentioned that this feature is of significant importance because the slightest distortion of the sheet portion passing the faceplate would result in defective copies.

A further feature for accomplishing the desired result with respect to automation and synchronization of the different steps involved in the presently discussed preferred 4 embodiment of this invention refers to the energization of the tube operating circuitry which is triggered or otherwise started when the leading edge of the sheet is engaged by the second pair of rollers which is that feeding the sheet by a pulling action.

Continuing the description of the illustrative embodiment, reference will now be made to the developing section of the reproduction apparatus of the present invention. This section includes a novel powder applicator including a closed-loop conduit through which particulate material is circulated. One portion of the conduit is formed by a container having an elongated aperture, and the sheet carrying the charge pattern is passed along this aperture. The conduit includes a blower for conveying the particulate material by an airstream inside and along the elongated container and across the aperture, so that the particles are attracted toward charged areas on the sheet. As the result of convection, the particles assume electrostatic charges due to friction with the walls of the conduit. It has been found that the use of such directed airstream results in an improved contrast image because the airstream acts to remove particulate material which otherwise might be deposited on non-charged areas. In other words, the airstream combines two functions which are: conveying the particulate material through the container and thereby crosswise along the charged surface of the sheet, and at the same time it acts as a cleaner or scavenger of the non charged areas so that maximum contrast is achieved in the finished image.

The powder applicator of the illustrative embodiment presently described suitably includes an additional feature for effectively preventing spilling of the powder. In accordance with this feature, the volume enclosed by the elongated applicator container is maintained at a pressure slightly below atmospheric so that air is taken in through the mentioned elongated aperture which simultaneously forms the outlet opening for the powder, as stated above. A very small gap is provided between the recording sheet passed along the aperture and the edges of the aperture. As a result of the air intake due to the pressure difference between ambient atmospheric pressure and the low pressure within the container, the particles within the container, in addition to being conveyed by the airstream, are suspended, generally in an upward direction against gravity forces. When disregarding the convection by the airstream, the resulting cloud of particles suspended by the air intake against gravity forces resembles to a certain extent the phenomenon generally known and termed a fluidized 'bed." It will be apparent that the air intake prevents spilling of powder which otherwise might occur along the elongated aperture in the container. The air intake furthermore effectively conrtibutes to the scavenging action of the airstream itself and thereby assists in the achievement of contrasting copies.

In addition to the foregoing, the provision of a pressure difference resulting in the air intake figures prominently in the improved operation which is obtained, even when using individual sheets. As described in the foregoing, individual sheets are fed through the reproduction machine at spaced intervals so that under continuous operating conditions intervals exist during which no sheet is passed along the outlet and air intake aperture of the applicator container. During these intervals, a comparatively greater quantity of air is taken in through the aperture because there is no sheet passed along it. The air intake efliciently prevents spilling of particulate material through the aperture into the open which would otherwise occur if no air were drawn from outside into the applicator container.

In accordance with the invention, and in a somewhat broader aspect of the novel arrangement, an electrostatic reproduction machine of the type under consideration includes a cathode ray tube having a charge-transmissive faceplate, operating circuitry for running the tube and a feeder mechanism for transporting individual sheets across the faceplate, with the elements of the feeder mechanism and the circuitry connected in such a manner that, at

the moment when the sheet reaches the proper position, one or more of the following actions take place: the tube operating circuit is energized to supply signals to the tube in accordance with signals received from a transmitter which does not form part of this invention and need not further be described. Simultaneously, the pusing action which previously brought the sheet into the position where tube operation starts is stopped so that the sheet is passed across the faceplate by a pulling action exclusively; further, the above mentioned outer electrode is brought into the position in which the gap between it and the faceplate of the tube is substantially closed so that the sheet passes the faceplate in a predetermined position, resulting in the desirable smooth constant motion across the faceplate.

In accordance with one important feature of this invention, the above mentioned second pair of rollers which exerts the pulling action on the sheet includes a pair of contact elements, one of the elements being associated with one of the rollers, the second element being associated with the second roller, and both cooperating to close a circuit in the absence of a sheet fed through this second pair of rollers, the circuit controlling the above enumerated actions. Other features of the invention include a relay operated multi-contact switch, with the relay being controlled by the circuit which is normally closed but opened when a sheet a passed between the rollers. When this circuit is broken, the relay operates. Operation of one contact pair of the relay automatically removes one of the two rollers of the first pair of cooperating rollers from its engagement with the sheet, so that the pushing action stops when the pulling action exerted by the second pair of rollers is started.

Another contact pair of the multi-contact switch controls a solenoid-operated mechanism to move the outer electrode to its position adjacent the faceplate. A further contact pair of the relay may either directly close or indirectly trigger the signal source circuitry, so that the cathode ray tube starts operating.

Further features, referring to the section in which particulate material is applied to the charged sheet, include the closed-loop conduit mentioned above through which the power is circulated by means of a blower or the like.

In accordance with a further feature, the closed-loop conduit includes the distributing or applicator container having an elongated aperture or slot extending across the sheet at a location where it leaves the second pair of rollers. In accordance with the feature of slightly subatmospheric pressure discussed in the foregoing, the powder applicator section forming part of the present invention includes an area of restricted diameter in the closed-loop to separate a high-pressure section from -a low-pressure section. In accordance with this feature, an air outlet with a filter for retaining the powder is provided in the high pressure section, whereas the low pressure section includes the applicator container, as described in more detail below.

At this point it is noted that all of the features mentioned in the foregoing paragraph, together with those described in the following specific description, intimately cooperate to form an electrostatic reproduction machine using the xerographic developing method and specifically adapted for achieving optimum results in a fully automatic, synchronized manner when using individual sheets as the recording medium.

The novel features which are believed to be characteristic of the invention, both as to its organization and method construction and operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which one illustrative embodiment of the invention is disclosed, by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and descrip tion only and does not constitute a limitation of the invention.

In the drawing:

FIGURE 1 is a schematic, partly isometric view of a reproduction machine;

FIG. 2 is a cross sectional fractional view through a portion of the feeder mechanism, illustrating the outer electrode and the front end of the tube;

FIG. 3 is a cross section through the applicator container of FIG. 1; and

FIG. 4 is a partial, schematic, isometric view illustrating another embodiment with the tube and electrode in reversed position.

Similar or identical parts are designated by the same reference numerals throughout all of the figures.

Referring now specifically to FIG. 1, the reproduction machine of this invention includes two sections. In the first section, a charge pattern is applied to 'a sheet by passing it in front of a cathode ray tube and comprises two pairs of rollers, the tube itself, the outer electrode, and the circuitry and electrical components. All of the elements forming this section of the device are shown at the left-hand side of FIG. 1. The right-hand side illustrates the powder applicator composed of the closed loop conduit, an additional pair of rollers, and a heated roller for fixing the image.

Referring now to the left-hand section in FIG. 1 and also to FIG. 2, the cathode ray tube generally designated by reference numeral 10 includes a tubular stem section 12 and a head portion 14 terminating in a faceplate 16. As described above, a plurality of individual conductors 18 (FIG. 2) extend through the faceplate. The conductors are physically separated and also electrically insulated from each other.

The above mentioned outer electrode facing the faceplate 16 is formed from an elongated slightly bent metal strip 20. A plurality of indentations 22 are provided in the portion of electrode 20 facing the faceplate so that a number of individual slightly curved tongues 24 is formed. In order to provide pivoting suspension for the electrode 20, a pair of L-shaped brackets 26 and 28 may be secured to each end of the electrode. Each of the brackets carries a pivot, pivot 30 of bracket 26 being shown in FIG. 1 and pivot 32 of bracket 28 appearing in FIG. 2. The pivots are rotatably supported in a pair of bearings omitted in FIG. 1, one of the bearings, designated by reference numeral 34, being shown in FIG. 2. Coil springs 36 connected to the brackets urge the electrode 20 in the position shown in FIG. 2 in which no gap is formed between the electrode 20 and the faceplate 16 of the cathode ray tube 10. At this point, attention is directed to FIG. 4 showing the head portion of the tube and the electrode in a reversed position to better illustrate the arrangement and also to illustrate an alternative embodiment in which a charge pattern is applied to the other, lower side of a sheet.

Continuing the description of the left-hand section in FIG. 1, this section includes two pairs of rollers forming part of the sheet feeding mechanism. This mechanism includes the above mentioned first pair of rollers 40 and 42 at the loading side of the reproduction machine. FIG. 1 illustrates a sheet 44 of paper or any other suitable recording medium in the process of being fed into the gap now formed between the faceplate 16 and the outer electrode 20. In the case of paper or plastic film, it was found that good results are obtained when previously applying a metal coating to the surface of the recording medium which later contacts the electrode 20. At this stage, rollers 40 and 42 cooperate to frictionally engage sheet 44 as shown in FIG. 1. As schematically indicated, roller 40 is supported by a frame type mechanism including legs 46, 48 and 50. This frame is pivotally suspended as schematically indicated by pivots 52 and 54.

At the output side, which is the opposite side of the tube 10, there is mounted another pair of rollers 54 and 56. It will be understood that this pair of rollers operates to exert the pulling action on the sheet 44 of which the leading edge 58 is frictionally engaged by the rollers 54 and 56 after having passed the faceplate 16 of the tube.

The following now refers to the circuit elements involved in operating this section of the device in the manner generally discussed above.

In general terms, each of the rollers 54 and 56 includes a conductive portion positioned in such a manner that a circuit is closed when no sheet is present between the rollers but the circuit is opened when a sheet is passed between the rollers and separates the conductive portions one from another. In practice, it was found that a satisfactory arrangement of this type is obtained when roller 54 is formed of metal, for example steel, and the main portion of the roller 56 is at least coated with, or entirely made of rubber or the like to provide frictional engagement with the sheet to be fed and pulled across the faceplate of the tube. With this main portion of the surface of roller 56 being an insulator, the conductive portion of roller 56 is formed by a metallic cap. The cap includes a larger ring-shaped portion 60 having a diameter identical with that of roller 56 so that it normally makes contact with the metallic surface of roller 54. The cap includes an end portion 62 of restricted diameter which therefore does not contact the roller 54. Carbon brushes 64, in practice a pair of such brushes as shown in FIG. 2, cooperate with the restricted diameter portion 62 of the cap for connection with the circuitry controlling the elements of the assembly, as described below.

Referring now to the circuitry and electric arrangements for obtaining the actions generally discussed above, a control circuit energized by power supply 72 through a main switch 74 includes the coil of a relay 76, line 78, brushes 64, cap 60, 62, roller 54, with the circuit being closed through ground connections 79 and 80. It will be seen that the circuit so described is closed and relay 76 energized in the absence of a sheet between rollers 54 and 56. Under these conditions, illustrated in FIG. 1, the energized relay 76 maintains a multi-contact switch or number of switches in a predetermined position. Three switches, designated 82, 84 and 86, are shown in this figure in the position corresponding to the requirements when sheet 44 is engaged by the first pair of rollers 40 and 42 but has not reached the second pair of rollers 54 and 56. At this stage, switch 82 is maintained open and a coil operated electromagnetic actuator 88 remains deenergized. As illustrated in FIG. 1, the armature 90 of the actuator is mechanically linked to the frame type support 46, 48, 50 which controls the position of roller 40. With switch 82 in the open position, the armature 90 is in the position shown in FIG. 1 and roller 40 frictionally engages the sheet 44 by cooperation with roller 42 to forward the sheet by pushing the leading edge 58 toward the gap between faceplate 16 and electrode 20.

Referring now to the second switch 84 controlled by relay 76, this switch forms part of a circuit energizing a similar coil operated actuator 92 having an armature 94 mechanically connected to the L-shaped brackets 26 and 28 secured to the outer electrode 20. With reference to FIG. 2, this figure illustrates in more detail the actuator 92 with armature 94 linked to the L-shaped bracket 28 by means of pivot 96. It can be seen that, when relay 76 is energized, switch 84 is closed and actuator 92 is energized, so that the brackets 26 and 28 the electrode 20 are tilted about pivots 30, 32 against the action of spring 36. Thus, the electrode is maintained in a position forming a gap between itself and the faceplate 16 (FIG. 1), and the leading edge 58 of sheet 44 is readily pushed into the gap and past the faceplate 16 under the action of rollers 40 and 42. In other words, the electrode 20, by virtue of its shape and position, acts as a guide for safely introducing the leading edge 58 of the sheet 44 when it is pushed toward the faceplate 16 under the action of rollers 40 and 42.

During this initial period of operation, switch 86 remains open and therefore the circuit including the signal source 100 and line 103 also remains open. At this point it should be noted that, for practical reasons, the power circuit 102 may remain energized throughout the entire operation and be controlled exclusively by the main switch 74. Alternatively, the power circuit 102, connected to the cathode ray tube through line 101, as well as the signal source circuitry 100, may be controlled by switch 86.

It is now assumed that the sheet 44 has been pushed by the roller pair 40, 42 across the faceplate 16, through the gap between the outer electrode 20 and the faceplate, and the leading edge 58 is actually engaged by the rollers 54 and 56. At this moment, the sheet 44 separates the annular portion 60 of the cap from roller 54 and thereby breaks the circuit controlling relay 76. From this moment, and until the sheet is completely passed through the roller pair 54, 56, relay 76 remains deenergized. In this regard, it should be stated that the specific design of cap 60, 62 insures flawless operation of the device inasmuch as the contacting area represented by the annular portion 60 is located in a position away from the very end of roller 54, so that the energizing circuit for relay 76 is interrupted even when the sheet 44 is not passed with extreme accuracy with respect to axial displacement between the rollers 54 and 56, as would be necessary when the contact elements were positioned at the end of the rollers. It will be apparent that any other suitable arrangement may be substituted for the same purpose. By way of example, rollers 54 and 56 may be provided with conductive areas at any location along their axes, and connection with line 78 may be made in any convenient manner known in the art, instead of using brushes.

Under the assumption that the leading edge 58 has reached its position where it is frictionally engaged by the rollers 54 and 56, the deenergized relay 76 closes switches 82 and 86 and opens switch 84. With switch 82 closed the electromagnetic actuator 88 becomes energized and armature 90 exerts a pulling action on the frame 46, 48 and 50 in the downward direction of FIG. 1, so that the frame is tilted about pivots 52, 54 and roller 40 is shifted into a position in which it is disengaged from sheet 44 or roller 42. Even though the driving mechanism (not shown) for the rollers continues operating, the pushing action previously exerted on the sheet 44 ceases, and the sheet 44 continues its motion exclusively under the pulling action of rollers 54 and 56.

At the same moment when relay 76 is deenergized and switch 82 closed, switch 84 is opened, thereby energizing actuator 92 to release armature 94 and with it the outer electrode 20 which now, under the action of spring 36, assumes a position in which it maintains the moving sheet 44 under gentle pressure against the faceplate 16 of the tube. This position of the electrode 20 is shown in FIG. 2, however with the sheet omitted.

At this point it may be mentioned that, in practice, the actuator 88 and its armature 90 are of the same nature as that of device 92 and armature 94 shown in FIG. 2 and operating in a similar manner, as will readily be understood.

In addition to the actuation of switches 82 and 84, relay 76, when'energized, closes switch 86 thereby triggermg or energizing the signal source circuit 100, so that the tube actually starts applying charge patterns to the sheet 44. It will be noted that, if no delay action occurs, the distance between rollers 54 and 56 and the faceplate determines the upper margin between edge 58 and the beginning of the charge pattern.

As indicated at 104 in FIG. 4, the outer electrode 20 is connected to ground. This ground connection is the result of practical considerations inasmuch as cathode ray tubes of this type are operated with a strong negative potential applied to the cathode of the electron gun, while the anode and the outer tube envelope are maintained at ground potential. This is so for purposes of safety, considering that voltages in the range of about 15,000 to 25,000 kilowatts are applied to the tube. Ac-

cordingly, the ground connection 104 renders the electrode 20 positive with respect to the cathode in the tube, and, consequently, the electrode 20 acts as an accelerating electrode with respect to the negative electrical charges transferred through the individual wire sections 18 across the faceplate 16.

The following new refers to the right-hand section in FIG. 1 illustrating the developer for rendering visible the latent charge pattern present on the sheet when it leaves the roller pair 54 and 56.

The powder applicator serving as the developer includes a number of elements in a circulation arrangement to form a closed-loop of conduits interconnecting the elements. The driving power for circulating particulate material or powder is supplied by a blower 106 or any other suitable equivalent device, such as a fan for example. The blower 106 produces an air stream conveying particulate material through pipeline 108 into a zone from which air may escape into the ambient atmosphere, with the particulate material being retained in the zone. Such element is illustrated in FIG. 1 as a cylindrical container 110 having a number of openings 112 in its wall and lined with any suitable filtering material, such as that used in vacuum cleaner bags, indicated by reference numeral 114. The outlet side of container 110 is connected by pipeline 116 to an area of restricted diameter 118 which, in turn, is connected through pipeline 120 to an applicator container 122. The closed-loop conduit is completed by pipelines 124 and 126 to return particulate material to the inlet of blower 106. A funnel-shaped additional branch of the pipe system is shown at 128 to permit refilling the closed-loop system with particulate material. In this regard, any of the powder conventional in xerography may be used, and good results have been obtained with pulverized hard rubber or plastic material. It should be noted that particulate material assuming a positive charge as a result of friction with the walls of the closed-loop system and with other particles may be preferred because positively charged particles adhere better to the negatively charged areas of the sheet.

Considering that the reproduction machine contemplated herein is especially designed for continuous operation, and also for the purpose of illustration, a second sheet 130 is shown in FIG. 1 in a position in which it is passed through the developing section of the apparatus. It will be understood that in this position the charge pattern has previously been applied to the sheet 130, i.e. it is assumed that, when in this position shown, sheet 130 has been passed through the feeder mechanism and in front of the faceplate 16, whereby a charge pattern has been applied to it.

Referring now specifically to the applicator tube 122, it has a shape of an elongated cylinder having a portion cut ofi in its bottom to form a slot-shaped aperture extending through almost its entire length. FIG. 3 is a cross sectional view through tube 122, illustrating in some detail the configuration of the applicator tube and the airstream conditions within it and in the surrounding area. The applicator tube or container 122 is provided with an elongated longitudinal slot 132 along its bottom, the slot forming the outlet opening for the particulate material. When the charged sheet 130 is passed along the slot 132, particles conveyed by the airstream through the applicator container or tube 122 are attracted toward charged areas on the sheet 130 and adhere there to render visible the latent charge pattern.

In addition to the simple electrostatic attraction of the powdered material, two more effects are achieved by the arrangement described and illustrated.

In the first place, and as a result of the powder being continuously circulated in the direction of arrows 134, FIG. 1, there is a continuous airflow longitudinally through the applicator tube 122. Whereas particulate material adheres to charged areas on the sheet 130, the airflow continuously cleans or scavenges non-charged areas, so

19 that particulate material adheres only to charged areas with practically no deposit at all on the non-charged areas. As a result, higher contrast images are obtained, as compared to reproduction devices using a stationary bed of powder.

The second effect is a result of the above mentioned portion 118 of restricted diameter in the closed-loop conduit. The restriction 118 separates a high-pressure section including the container from a low-pressure section in which slightly subatmospheric pressure prevails and which comprises the powder applicator tube 122. As a result, air is taken in around the edges 138 of slot 132, FIG. 3, as indicated by arrows 136. It will be understood that the additional air taken in is expelled again in the high-pressure section through filter 114 and openings 112, however without expelling powder, due to the action of the filter 114. In order to permit the air intake around the edges 138, conventional guides for the sheet may be provided for spacing the sheet from the edges to leave very small gaps between the sheet 130 and the edges 138. At this point it should be noted that such guides in the vicinity of applicator tube 122, as well as numerous other guides for properly directing the sheets through the entire apparatus, have been omitted for the sake of simplification.

The comparatively complex action of the air intake represented by arrows 136, FIG. 3, will now be discussed in some detail. In connection with the phenomenon of airflow within applicator tube 122, reference is made to the equilibrium state between gravity forces on particulate material and the force applied to it by an upwardly directed airflow. Particulate material, when suspended in such state of equilibrium is frequently referred to as a fluidized bed. When applying the concept of the fluidized bed to the conditions prevailing within the applicator tube 122 it can be seen that the air intake occurring in the direction of arrows 136 tends to suspend the particles conveyed in the tube to prevent them from deposition on the sheet 130. As a matter of course, this action is greater in the vicinity of the edges 138 as it is in the center of the slot. It will be observed that the suspending action of the air intake occurs in addition and independently of convection of particulate material axially through applicator 122 because they form a right angle one with the other. In other words, and referring now to FIG. 3, the suspension action occurs upwardly with-in the plane of the paper, whereas the airstream conveying the particulate material occurs in a direction perpendicular to the plane of the paper. It will be furthermore understood that, in the absence of a sheet 130, and with the slot 132 remaining open, the air intake prevents any significant spilling of particulate material.

The desired balance condition between air stream and air intake will depend on numerous parameters such as the nature of the particulate material. The system is therefore suitably adjustable and, to this effect, the blower speed may be controlled. Furthermore, the diameter of the restricted area 118 may be made adjustable and it is readily understood that, in practice, a reducing valve may be used for providing an adjustable cross section in the closed-loop conduit.

Summarizing, the pressure difference between the ambient atmosphere and that inside the applicator tube 122 resulting in an air intake along the edges of the slot significantly contributes to an improvement of the resulting copies with respect to contrast, and furthermore assists in the prevention of undesirable loss of particulate material during the intervals when no sheet is passed through the applicator section.

For the sake of completeness, FIG. 1 illustrates a roller 140 which may be heated by any convenient conventional means for the purpose of fixing the powder image on the sheet 130. This fixing step is well known in the art. By Way of example, the particulate material may be made of thermoplastic material which fuses onto the sheet under the heating action of the roller 140. Alternatively, and for example when using pulverized hard rubber, the sheet 1 i may be impregnated or coated with thermoplastic material.

An additional pair of rollers 142 and 144 is shown to indicate the mechanism necessary for pulling the sheet 130 across the powder applicator tube 122 and, as stated above, numerous further elements including driving mechanisms for the rollers and guides for the sheets 44 and 130 have been omitted in the drawing for the sake of simplification.

In the embodiment illustrated in FIGS. 13, the cathode ray tube is mounted in a position with the faceplate pointing downwardly. However, and as one of the numerous alternatives of the present invention, the tube neck 12 may point downwardly, with the faceplate pointing in an upward direction. Then, the sheets are passed in a horizontal plane above the faceplate, and the electrode 20 is mounted and actuated in a reversed manner. Such an arrangement omitting the sheet is shown in FIG. 4. Considering that, otherwise, the feeding mechanism and the circuitry employed are unchanged as compared to the embodiment shown in FIGS. 1-3, all of these components have been omitted in FIG. 4, with the reference numerals being identical with those used above.

With regard to the powder applicator, it is readily understood that, since then the charge pattern is applied to the downwardly facing side of the sheets, the applicator tube or container 122 must also be reversed, i.e. the slot 132 must point upwardly and the sheet is passed above it instead of below. Then the air intake also assumes the functions described above, with the exception that its direction in the tube 122 coincides with that of gravity forces which are overcome by a comparatively increased blower activity. Under these circumstances, the term fluidized bed does not properly apply anymore. However, the essential characteristics with respect to prevention of spilling powder and cleansing of non-charged areas are the same.

It is to be understood that the above described arrangements are illustrative of the application of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention. Thus, by way of example and not of limitation, endless belts may be used instead of rollers for feeding the sheets through either of the sections of the reproduction machine. Numerous different contact arrangements may be designed and substituted for the cap 60, 62 to produce the same result which would be either closing or breaking a circuit to actuate switches 82, 84 and 86. As stated above, switch 86 may be connected to energize the signal source circuitry, as shown, or else a triggering action initiated by a signal may be found preferable. In this case, upon triggering, signals are supplied to the tube for a predetermined period of time which may comprise a complete series of signals to deposit a complete image on one sheet, with the signal source being stopped until the next sheet reaches the corresponding position, and the signal source is again triggered to repeat the same series of signals. Although it has been found convenient to use a closedloop conduit in the powder applicator section of the reproduction machine, different arrangements may be made for supplying particulate material to the applicator tube 122. Accordingly, from the foregoing remarks, it is to be understood that the present invention is to be limited only by the spirit and scope of the appended claims.

What is claimed is:

1. In an electrostatic reproduction machine:

a cathode ray tube having a charge-transmissive faceplate,

an outer electrode facing the faceplate for both guiding a sheet across from one side to the other side of the faceplate and applying an accelerating potential to signal charges transferred through the faceplate to apply a charge pattern to the sheet,

means for spacing the outer electrode from the faceplate to form a gap between them,

a first pair of cooperating rollers rotatably mounted at said one'side of the faceplate for frictionally engaging the sheet to advance it across the faceplate and through the gap by a pushing action,

a second pair of cooperating rollers rotatably mounted at said other side of the faceplate for pulling the sheet across the faceplate,

means for disengaging at least one roller of the first roller pair for the period of time during which the second roller pair engages the sheet,

means for releasing the spacing means to substantially close the gap also for said period of time, and

means for developing the charge pattern applied to the sheet, said developing means comprising (a) a closed-loop conduit,

(b) blower means in the conduit for circulating powder through the conduit by means of an air stream,

(0) a pressure reducing area of restricted diameter in the conduit for separating a high-pressure section from a low-pressure section,

(d) the high-pressure section including a filterlined air escape for decreasing the quantity of air in the stream but retaining the powder in the stream,

(e) an elongated tubular container forming part of the low-pressure section, the container having an elongated opening forming an air intake to prevent undesirable powder escape, and

(f) means for passing the sheet with the charge pattern past the opening to cause powder to be electrostatically attracted toward and to adhere to charged sheet areas.

2. In a powder applicator for developing latent charge patterns previously applied to a sheet,

(A) a closed-loop conduit, including (a) blower means for circulating powder through the conduit by means of an airstream,

(b) a pressure reducing area of restricted diameter in the conduit for separating a high-pressure section from a low-pressure section,

(c) the high-pressure section including a filterlined air escape for decreasing the quantity of air in the stream but retaining the powder in the stream, an elongated tubular container forming part of the low-pressure section, the container having at least one elongated opening for forming an air intake to prevent undesirable powder escape; and

(B) means for passing the sheet across the opening to cause powder to be electrostatically attracted toward and to adhere to charged sheet areas,

3. In an electrostatic reproduction machine,

a cathode ray tube having an elongated charge-transmission faceplate,

circuitry for operating the cathode ray tube,

an elongated outer electrode mounted to coextend parallel with the faceplate for both guiding a sheet from one side across the faceplate to the other side and also for applying an accelerating potential to signal charges transferred through the faceplate and onto the sheet,

means for frictionally engaging the sheet at said other side to pull it across the faceplate,

means for normally spacing the outer electrode from the faceplate to form a gap between them, means for temporarily releasing the spacing means to substantially close the gap,

means for actuating the releasing means for the period of time during which the pulling means engage the sheet, and

means for energizing the tube operating circuitry for the same period of time.

4. In an electrostatic reproduction machine,

a cathode ray tube having an elongated charge-transmissive faceplate,

an elongated outer electrode mounted to coextend parallel with the faceplate for both guiding a sheet from one side across the faceplate to the other side and also for applying an accelerating potential to signal charges transferred through the faceplate and onto the sheet,

means for frictionally engaging the sheet at said other side to pull it across the faceplate,

means for normally spacing the outer electrode from the faceplate to form a gap between them,

means for temporarily releasing the spacing means to substantially close the gap, and

means for actuating the releasing means for the period of time during which the pulling means engage the sheet.

5. In an electrostatic reproduction machine,

cathode ray tube having a charge-transmissive elongated faceplate,

a pair of rollers for pulling a sheet across the faceplate,

an annular contact element secured to one of the rollers and cooperating with a conductive portion of the other roller,

switching means energized through the contact element and the conductive portion of said other roller, with the energizing circuit being opened when a sheet is fed through the roller pair to separate the contact element from said conductive portion of the other rollers, and the circuit being closed in the absence of a sheet,

circuitry for operating the cathode ray tube, and

means controlled by said switching means for enabling the tube operating circuitry.

6. In an electrostatic reproduction machine,

a cathode ray tube having a charge-transmissive faceplate,

circuitry for operating the cathode ray tube to apply a charge pattern to a sheet,

a first pair of rollers for frictionally engaging the sheet and positioned at one side of the faceplate for advancing the sheet toward the faceplate by a pushing action,

a second pair of rollers located at the opposite side of the faceplate for frictionally engaging the leading edge of the sheet to further advance and feed the sheet across and past the faceplate,

means for energizing the tube operating circuit upon engagement of the sheet by the second roller pair and for the duration of said engagement, said means including a pair of cooperating contacts, each contact forming part of one of the rollers of the second pair, whereby a sheet engaged between the rollers separates the contacts, and

means for disengaging at least one roller of the first roller pair for the same duration.

7. In an electrostatic reproduction machine,

a cathode ray tube having a charge-transmissive faceplate, 1

an outer electrode facing the faceplate for both guiding a sheet across the faceplate from one side to the other .side and applying an accelerating potential to signal charges transferred through the faceplate and on to the sheet,

means for spacing the outer electrode from the face- :plate to form a gap between them,

a first pair of cooperating rollers rotatably mounted at said one side of the faceplate for frictionally engaging the sheet to advance it across the faceplate and through the gap by a pushing action, I

a second pair of cooperating rollers rotatably mounted at said other side of the faceplate for pulling the sheet across the faceplate,

means for disengaging at least one roller of the first roller pair for the period of time during which the second roller pair engages the sheet, and

means for releasing the spacing means to substantially close the gap also for said period of time.

8. In an electrostatic reproduction machine,

a cathode ray tube having a charge-transmissive facep ate,

circuitry for operating the cathode ray tube to apply a charge pattern to a sheet,

a first pair of rollers for frictionally engaging the sheet and positioned at one side of the faceplate for advancing the sheet toward the faceplate by a pushing action,

a second pair of rollers located at the opposite side of the faceplate for frictionally engaging the leading edge of the sheet to further advance and pull the sheet across the faceplate,

an elongated outer electrode mounted to coextend parallel with the faceplate for both guiding the sheet from one side across the faceplate to the other side and also for applying an accelerating potential to signal charges transferred through the faceplate and onto the sheet,

means for normally spacing the outer electrode from the faceplate to form a gap between them,

means for temporarily releasing the spacing means to substantially close the gap,

means for actuating the releasing means for the period of time during which the second pair of rollers engages the sheet,

means for disengaging at least one roller of the first roller pair for the same period of time, and

means for enabling the cathode ray tube operating circuitry also for the same period of time,

9. In an electrostatic reproduction machine,

a cathode ray tube having an insulating elongated faceplate and a plurality of wire conductors extending through and individually embedded in the faceplate,

circuit means for operating the tube,

an outer spring-loaded elongated electrode coextending parallel with and facing the faceplate to form a guide for passing a sheet across the faceplate and also for applying an accelerating potential to signal charges transferred through the faceplate and onto the sheet in accordance with signals applied to the cathode ray tube,

electrical coil-operated means for maintaining the outer electrode spaced from the faceplate against the action of the spring to form a gap between the electrode and the faceplate,

a first pair of cooperating rollers rotatably mounted to extend adjacent, parallel and at one side of the faceplate for advancing a sheet across the faceplate and through the gap by a pushing action,

a second pair of cooperating rollers rotatably mounted to extend parallel and adjacent at the other side of the faceplate for pulling the advanced sheet across the faceplate,

an annular contact element secured to one of the rollers of the second pair and cooperating with a conductive portion of the other roller of the second pair,

first switching means energized through the contact element and the conductive portion of said other roller of the second roller pair, with the energizing circuit being opened when a sheet is fed through the second roller pair to separate the contact element from said conductive portion of the other roller, and the circuit being closed in the absence of a sheet, and

additional switching means controlled by the first switching means for performing all three of the following actions for the duration of a sheet being fed through the second roller pair:

(a) enabling the cathode ray tube operating circuit;

(b) de-energizing the coil-operated spacing means to cause the gap between the outer electrode and the faceplate to substantially close under the .action of the spring; and

(c) disengaging one roller of the first roller pair,

15" 16 whereby the pushing action is caused to stop, the 2,890,923 6/ 1959 Huebner 346-74 sheet being fed through the machine exclusively 2,932,548 4/ 1960 Nau et a1 346-74 by the pulling action, 3,001,848 9/1961 Walkup 250-49.5 3,001,849 9/1961 Walkup 250-49.5 References Cited by the Examiner 5 3,008,826 11/ 1961 Mott et a1.

UNITED STATES PATENTS 3,164,738 1/1965 Fyler 31373 Young et a1. BERNARD KONICK, Primary Examiner. 2771336 11/1956 fig g RALPH G. NILSON, IRVING SRAGOW, Examiners. 2,777,745 1/1957 McNaney 250-495 10 H. s. MILLER, A. F. BERNARD, Assistant Examiners. 

1. IN AN ELECTROSTATIC REPRODUCTION MACHINE: A CATHODE RAY TUBE HAVING A CHARGE-TRANSMISSIVE FACEPLATE, AN OUTER ELECTRODE FACING THE FACEPLATE OF BOTH GUIDING A SHEET ACROSS FROM ONE SIDE TO THE OTHER SIDE OF THE FACEPLATE AND APPLYING AN ACCELERATING POTENTIAL TO SIGNAL CHARGES TRANSFERRED THROUGH THE FACEPLATE TO APPLY A CHARGE PATTERN TO THE SHEET, MEANS FOR SPACING THE OUTER ELECTRODE FROM THE FACEPLATE TO FORM A GAP BETWEEN THEM, A FIRST PAIR OF COOPERATING ROLLERS ROTATABLY MOUNTED AT SAID ONE SIDE OF THE FACEPLATE FOR FRICTIONALLY ENGAGING THE SHEET TO ADVANCE IT ACROSS THE FACEPLATE AND THROUGH THE GAP BY A PUSHING ACTION, A SECOND PAIR OF COOPERATING ROLLERS ROTATABLY MOUNTED AT SAID OTHER SIDE OF THE FACEPLATE FOR PULLING THE SHEET ACROSS THE FACEPLATE, MEANS FOR DISENGAGING AT LEAST ONE ROLLER OF THE FIRST ROLLER PAIR FOR THE PERIOD OF TIME DURING WHICH THE SECOND ROLLER PAIR ENGAGES THE SHEET, MEANS FOR RELEASING THE SPACING MEANS TO SUBSTANTIALLY CLOSE THE GAP ALSO FOR SAID PERIOD OF TIME, AND MEANS FOR DEVELOPING THE CHARGE PATTERN APPLIED TO THE SHEET, AND DEVOPLING MEANS COMPRISING (A) A CLOSED-LOOP CONDUIT, (B) BLOWER MEANS IN THE CONDUIT FOR CIRCULATING POWDER THROUGH THE CONDUIT BY MEANS OF AN AIR STREAM, (C) A PRESSURE REDUCING AREA OF RESTRICTED DIAMETER IN THE CONDUIT FOR SEPARATING A HIGH-PRESSURE SECTION FROM A LOW-PRESSURE SECTION, (D) THE HIGH-PRESSURE SECTION INCLUDING A FILTERLINED AIR ESCAPE FOR DECREASING THE QANTITITY OF AIR IN THE STREAM BUT RETAINING THE POWDER IN THE STREAM, (E) AN ELONGATED TUBULAR CONTAINER FORMING PART OF THE LOW-PRESSURE SECTION, THE CONTAINER HAVING AN ELONGATED OPENING FORMING AN AIR INTAKE TO PREVENT UNDESIRABLE POWDER ESCAPE, AND (F) MEANS FOR PASSING THE SHEET WITH THE CHARGE PATTERN PAST THE OPENING TO CAUSE POWDER TO BE ELECTROSTATICALLY ATTRACTED TOWARD AND TO ADHERE TO CHARGED SHEET AREAS. 